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  <title>Document</title>
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  <!--  i j
        0 4  第一趟比4次:0和1,1和2
        1 3
        2 2
        3 1
  j < length - i - 1 -->
  <script>
    let arr = [9, 8, 7, 6, 5, 4, 3, 2, 1]
    // [8, 7, 6, 5, 4, 3, 2, 1, 9]
    // [5, 1, 8, 9, 2, 6, 4]
    for (let i = 0; i < arr.length - 1; i++) {
      for (let j = 0; j < arr.length - i - 1; j++) {
        if (arr[j] > arr[j + 1]) {
          let tep = arr[j]
          arr[j] = arr[j + 1]
          arr[j + 1] = tep
        }
      }
    }
    document.write(arr)
  </script>
</body>

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